diff --git a/src/core/tools/__tests__/multiApplyDiffTool.spec.ts b/src/core/tools/__tests__/multiApplyDiffTool.spec.ts
new file mode 100644
index 0000000000..0bdedb9cd5
--- /dev/null
+++ b/src/core/tools/__tests__/multiApplyDiffTool.spec.ts
@@ -0,0 +1,401 @@
+import { applyDiffTool } from "../multiApplyDiffTool"
+import { EXPERIMENT_IDS } from "../../../shared/experiments"
+import * as fs from "fs/promises"
+import * as fileUtils from "../../../utils/fs"
+import * as pathUtils from "../../../utils/path"
+
+// Mock dependencies
+vi.mock("fs/promises")
+vi.mock("../../../utils/fs")
+vi.mock("../../../utils/path")
+vi.mock("../../../utils/xml")
+vi.mock("../applyDiffTool", () => ({
+	applyDiffToolLegacy: vi.fn(),
+}))
+
+// Mock TelemetryService
+vi.mock("@roo-code/telemetry", () => ({
+	TelemetryService: {
+		get instance() {
+			return {
+				trackEvent: vi.fn(),
+				trackError: vi.fn(),
+				captureDiffApplicationError: vi.fn(),
+			}
+		},
+	},
+}))
+
+describe("multiApplyDiffTool", () => {
+	let mockCline: any
+	let mockBlock: any
+	let mockAskApproval: any
+	let mockHandleError: any
+	let mockPushToolResult: any
+	let mockRemoveClosingTag: any
+	let mockProvider: any
+
+	beforeEach(() => {
+		vi.clearAllMocks()
+
+		mockProvider = {
+			getState: vi.fn().mockResolvedValue({
+				experiments: {
+					[EXPERIMENT_IDS.MULTI_FILE_APPLY_DIFF]: true,
+				},
+				diagnosticsEnabled: true,
+				writeDelayMs: 0,
+			}),
+		}
+
+		mockCline = {
+			providerRef: {
+				deref: vi.fn().mockReturnValue(mockProvider),
+			},
+			cwd: "/test",
+			taskId: "test-task",
+			consecutiveMistakeCount: 0,
+			consecutiveMistakeCountForApplyDiff: new Map(),
+			recordToolError: vi.fn(),
+			say: vi.fn().mockResolvedValue(undefined),
+			sayAndCreateMissingParamError: vi.fn().mockResolvedValue("Missing parameter error"),
+			ask: vi.fn().mockResolvedValue({ response: "yesButtonClicked", text: "", images: [] }),
+			diffStrategy: {
+				applyDiff: vi.fn().mockResolvedValue({
+					success: true,
+					content: "modified content",
+				}),
+				getProgressStatus: vi.fn(),
+			},
+			diffViewProvider: {
+				reset: vi.fn().mockResolvedValue(undefined),
+				editType: undefined,
+				originalContent: undefined,
+				open: vi.fn().mockResolvedValue(undefined),
+				update: vi.fn().mockResolvedValue(undefined),
+				scrollToFirstDiff: vi.fn(),
+				saveDirectly: vi.fn().mockResolvedValue(undefined),
+				saveChanges: vi.fn().mockResolvedValue(undefined),
+				pushToolWriteResult: vi.fn().mockResolvedValue("File modified successfully"),
+			},
+			api: {
+				getModel: vi.fn().mockReturnValue({ id: "test-model" }),
+			},
+			rooIgnoreController: {
+				validateAccess: vi.fn().mockReturnValue(true),
+			},
+			rooProtectedController: {
+				isWriteProtected: vi.fn().mockReturnValue(false),
+			},
+			fileContextTracker: {
+				trackFileContext: vi.fn().mockResolvedValue(undefined),
+			},
+			didEditFile: false,
+		} as any
+
+		mockAskApproval = vi.fn().mockResolvedValue(true)
+		mockHandleError = vi.fn()
+		mockPushToolResult = vi.fn()
+		mockRemoveClosingTag = vi.fn((tag, value) => value)
+
+		// Mock file system operations
+		;(fileUtils.fileExistsAtPath as any).mockResolvedValue(true)
+		;(fs.readFile as any).mockResolvedValue("original content")
+		;(pathUtils.getReadablePath as any).mockImplementation((cwd: string, path: string) => path)
+	})
+
+	describe("Early content validation", () => {
+		it("should filter out non-string content at parse time", async () => {
+			mockBlock = {
+				params: {
+					args: `<file>
+						<path>test.ts</path>
+						<diff>
+							<content>valid string content</content>
+						</diff>
+					</file>`,
+				},
+				partial: false,
+			}
+
+			// Mock parseXml to return mixed content types
+			const parseXml = await import("../../../utils/xml")
+			;(parseXml.parseXml as any).mockReturnValue({
+				file: {
+					path: "test.ts",
+					diff: [
+						{ content: "<<<<<<< SEARCH\ntest\n=======\nreplaced\n>>>>>>> REPLACE" },
+						{ content: null },
+						{ content: undefined },
+						{ content: 42 },
+						{ content: "" }, // Empty string should also be filtered
+						{ content: "<<<<<<< SEARCH\nmore\n=======\nchanges\n>>>>>>> REPLACE" },
+					],
+				},
+			})
+
+			await applyDiffTool(
+				mockCline,
+				mockBlock,
+				mockAskApproval,
+				mockHandleError,
+				mockPushToolResult,
+				mockRemoveClosingTag,
+			)
+
+			// Should complete without error and only process valid string content
+			expect(mockPushToolResult).toHaveBeenCalled()
+			expect(mockHandleError).not.toHaveBeenCalled()
+
+			// Verify that only valid diffs were processed
+			const resultCall = mockPushToolResult.mock.calls[0][0]
+			// Should not include the single block notice since we have 2 valid blocks
+			expect(resultCall).not.toContain("Making multiple related changes")
+		})
+	})
+
+	describe("SEARCH block counting with non-string content", () => {
+		it("should handle diffItem.content being undefined", async () => {
+			mockBlock = {
+				params: {
+					path: "test.ts",
+					diff: undefined, // This will result in undefined content
+				},
+				partial: false,
+			}
+
+			await applyDiffTool(
+				mockCline,
+				mockBlock,
+				mockAskApproval,
+				mockHandleError,
+				mockPushToolResult,
+				mockRemoveClosingTag,
+			)
+
+			// Should complete without throwing an error
+			expect(mockPushToolResult).toHaveBeenCalled()
+			expect(mockHandleError).not.toHaveBeenCalled()
+		})
+
+		it("should handle diffItem.content being null", async () => {
+			mockBlock = {
+				params: {
+					args: `<file>
+						<path>test.ts</path>
+						<diff>
+							<content></content>
+						</diff>
+					</file>`,
+				},
+				partial: false,
+			}
+
+			// Mock parseXml to return null content
+			const parseXml = await import("../../../utils/xml")
+			;(parseXml.parseXml as any).mockReturnValue({
+				file: {
+					path: "test.ts",
+					diff: {
+						content: null,
+					},
+				},
+			})
+
+			await applyDiffTool(
+				mockCline,
+				mockBlock,
+				mockAskApproval,
+				mockHandleError,
+				mockPushToolResult,
+				mockRemoveClosingTag,
+			)
+
+			// Should complete without throwing an error
+			expect(mockPushToolResult).toHaveBeenCalled()
+			expect(mockHandleError).not.toHaveBeenCalled()
+		})
+
+		it("should handle diffItem.content being a number", async () => {
+			mockBlock = {
+				params: {
+					args: `<file>
+						<path>test.ts</path>
+						<diff>
+							<content>123</content>
+						</diff>
+					</file>`,
+				},
+				partial: false,
+			}
+
+			// Mock parseXml to return number content
+			const parseXml = await import("../../../utils/xml")
+			;(parseXml.parseXml as any).mockReturnValue({
+				file: {
+					path: "test.ts",
+					diff: {
+						content: 123, // Number instead of string
+					},
+				},
+			})
+
+			await applyDiffTool(
+				mockCline,
+				mockBlock,
+				mockAskApproval,
+				mockHandleError,
+				mockPushToolResult,
+				mockRemoveClosingTag,
+			)
+
+			// Should complete without throwing an error
+			expect(mockPushToolResult).toHaveBeenCalled()
+			expect(mockHandleError).not.toHaveBeenCalled()
+		})
+
+		it("should correctly count SEARCH blocks when content is a valid string", async () => {
+			const diffContent = `<<<<<<< SEARCH
+old content
+=======
+new content
+>>>>>>> REPLACE
+
+<<<<<<< SEARCH
+another old content
+=======
+another new content
+>>>>>>> REPLACE`
+
+			mockBlock = {
+				params: {
+					path: "test.ts",
+					diff: diffContent,
+				},
+				partial: false,
+			}
+
+			await applyDiffTool(
+				mockCline,
+				mockBlock,
+				mockAskApproval,
+				mockHandleError,
+				mockPushToolResult,
+				mockRemoveClosingTag,
+			)
+
+			// Should complete successfully
+			expect(mockPushToolResult).toHaveBeenCalled()
+			const resultCall = mockPushToolResult.mock.calls[0][0]
+			// Should not include the single block notice since we have 2 blocks
+			expect(resultCall).not.toContain("Making multiple related changes")
+		})
+
+		it("should show single block notice when only one SEARCH block exists", async () => {
+			const diffContent = `<<<<<<< SEARCH
+old content
+=======
+new content
+>>>>>>> REPLACE`
+
+			mockBlock = {
+				params: {
+					path: "test.ts",
+					diff: diffContent,
+				},
+				partial: false,
+			}
+
+			await applyDiffTool(
+				mockCline,
+				mockBlock,
+				mockAskApproval,
+				mockHandleError,
+				mockPushToolResult,
+				mockRemoveClosingTag,
+			)
+
+			// Should complete successfully
+			expect(mockPushToolResult).toHaveBeenCalled()
+			const resultCall = mockPushToolResult.mock.calls[0][0]
+			// Should include the single block notice
+			expect(resultCall).toContain("Making multiple related changes")
+		})
+	})
+
+	describe("Edge cases for diff content", () => {
+		it("should handle empty diff array", async () => {
+			mockBlock = {
+				params: {
+					args: `<file>
+						<path>test.ts</path>
+						<diff></diff>
+					</file>`,
+				},
+				partial: false,
+			}
+
+			const parseXml = await import("../../../utils/xml")
+			;(parseXml.parseXml as any).mockReturnValue({
+				file: {
+					path: "test.ts",
+					diff: [],
+				},
+			})
+
+			await applyDiffTool(
+				mockCline,
+				mockBlock,
+				mockAskApproval,
+				mockHandleError,
+				mockPushToolResult,
+				mockRemoveClosingTag,
+			)
+
+			// Should complete without error
+			expect(mockPushToolResult).toHaveBeenCalled()
+			expect(mockHandleError).not.toHaveBeenCalled()
+		})
+
+		it("should handle mixed content types in diff array", async () => {
+			mockBlock = {
+				params: {
+					args: `<file>
+						<path>test.ts</path>
+						<diff>
+							<content>valid string content</content>
+						</diff>
+					</file>`,
+				},
+				partial: false,
+			}
+
+			const parseXml = await import("../../../utils/xml")
+			;(parseXml.parseXml as any).mockReturnValue({
+				file: {
+					path: "test.ts",
+					diff: [
+						{ content: "<<<<<<< SEARCH\ntest\n=======\nreplaced\n>>>>>>> REPLACE" },
+						{ content: null },
+						{ content: undefined },
+						{ content: 42 },
+						{ content: "<<<<<<< SEARCH\nmore\n=======\nchanges\n>>>>>>> REPLACE" },
+					],
+				},
+			})
+
+			await applyDiffTool(
+				mockCline,
+				mockBlock,
+				mockAskApproval,
+				mockHandleError,
+				mockPushToolResult,
+				mockRemoveClosingTag,
+			)
+
+			// Should complete without error and count only valid string SEARCH blocks
+			expect(mockPushToolResult).toHaveBeenCalled()
+			expect(mockHandleError).not.toHaveBeenCalled()
+		})
+	})
+})
diff --git a/src/core/tools/multiApplyDiffTool.ts b/src/core/tools/multiApplyDiffTool.ts
index 4cce2d1777..50695b1da7 100644
--- a/src/core/tools/multiApplyDiffTool.ts
+++ b/src/core/tools/multiApplyDiffTool.ts
@@ -135,13 +135,17 @@ export async function applyDiffTool(
 					let diffContent: string
 					let startLine: number | undefined
 
-					diffContent = diff.content
+					// Ensure content is a string before storing it
+					diffContent = typeof diff.content === "string" ? diff.content : ""
 					startLine = diff.start_line ? parseInt(diff.start_line) : undefined
 
-					operationsMap[filePath].diff.push({
-						content: diffContent,
-						startLine,
-					})
+					// Only add to operations if we have valid content
+					if (diffContent) {
+						operationsMap[filePath].diff.push({
+							content: diffContent,
+							startLine,
+						})
+					}
 				}
 			}
 		} catch (error) {